In plumbing installations, copper tubing has been widely employed. In risers, used for connecting tubing to fixtures or tanks, the end of the copper tubing is shaped to form a bulb sealing surface and such bulb includes a shoulder permitting the tubing and thus the bulb sealing surface to be drawn into biting or sealing engagement with the fixture. The cost of such copper tubing and the cost of forming it to permit the connection to such fixtures or tanks fluctuates frequently and widely and thus the cost may be substantial.
More recently, polybutylene has been approved for use in plumbing. Because of its flexibility, if it can properly be formed with the suitable bulb sealing surface, it is highly desirable as a tubing or plumbing material.
In order to provide such polybutylene tubing with a bulb sealing surface or an end cap for such purposes, a variety of techniques have been employed. A common technique is to employ a separately molded bulb which is spun-welded to the O.D. of the end of the tube. Another technique is to form a flange on the O.D. of the tube and again to insert a separately molded neoprene or like concave washer on the flange for sealing purposes. Both such processes have cost and performance drawbacks.
In applicant's above noted prior copending application, there is disclosed a method of reforming plastic tube end to form such bulb sealing surface with the projecting tube end to be reformed being heated externally. A pin or mandrel on one of the forming dies or molds fits within the tubing end to maintain the I.D. of the tubing during the forming operation. The tube is formed between mating dies or molds with the tube end projecting through one of the dies or molds and onto the guide pin or mandrel projecting from the other. The mold or die from which the pin projects is normally cooled or chilled which affects the temperature of the pin. In such process, the tube end to be formed is normally heated only externally and not uniformly radially from both its inside and outside surfaces. The process disclosed in such prior application, while producing satisfactory tube ends, may form minute fold lines on the interior of the tube end which indicate that the reformed tube end is not completely or integrally formed. Moreover, the heating and cooling steps of the prior process are somewhat counterproductive resulting in reduced production efficiencies and increased energy consumption.
In order to provide a completely integral formed tube end, it is desirable that the tube end be uniformly heated both from its interior and its exterior. The entire wall thickness of the tubing should be brought to a uniform forming temperature and this may not be achieved by heating the tubing simply externally. Since the mandrel or pin must protect the I.D. of the tube end during forming, it is desirable that the pin also be able to provide sufficient heat to obtain such uniform heating and yet be isolated or heat insulated from the cooling or forming mold from which it projects. It is also desirable that the pin not become or remain too hot that it cannot be withdrawn from the reformed tube end without affecting the quality of the interior or I.D. surface of the reformed tube end.